Controllable Synthesis And Electrochemical Properties Of TiO₂-based Nanocomposites

Titanium dioxide(Ti O2)has been widely applied in diverse applications,by virtue of their advantages including high surface area,excellent ion transport,and short path of electron transportation,however its poor specific capacitance and low electronity stopped its development in energy storage devices,such as supercapacitors.Ti O2-based nanocomposites could be well developed in potential research fields with the assistance of preparative strategies.However,there are some shortages in the preparative strategies of Ti O2-based nanocomposites,blocking their extension to potential fields.For instance,preparative methodology for accurately fabricating Ti O2-based nanocomposites is urgently needed;systematical investigations on Ti O2-based nanocomposites(One-dimensional-1D,Two-dimentional-2D and Three-dimensional-3D)are scarecely reported;in addition,the surface/interface physical and chemical properties need probed to direct the fabrication and application of Ti O2-based nanocomposites.In order to overcome these problems,fabrication techniques and supercapacitive performance are well addressed in this thesis.Various simple-but-effective and controllable methods(e.g.,one-pot hydrothermal method)and different composites(e.g.,Au-Ti O2,graphene-Ti O2,Mn O2-Ti O2)have been detailedly investigated for their applications in supercapacitors.The detailed experimental results can be summarized as follows.(1)Synthesis and supercapacitive properties of Mn Ox and their derives-decorated Ti grids nanocompositesTi grid not only has good anti-corrosion and conductivity,but has strong coheresion to enhance the composites.Here,Ti grid was chosen as current collectors,and Ti resource for Ti O2 nanoarrays.Interestingly,cobweb-like architecture on Ti grid is formed after surface modification,and ultrathin Mn O2 nanosheet arrays are homogenously covered on such cobweb-like architecture to enhance contact surface area and close connection between these components to promote ions penetration and electron transport.Such unique method for modifying the surface of the metal substrate to load transition metal oxide nanostructures can be extended to diverse substrates.Afterwards,Fe OOH as Mn Ox derives can be chemically transformed from Mn O2 nanostructure on Ti grids.Herein,the Fe OOH nanoarrays on the titanium grid have been first fabricated by a facile hydrothermal method for advanced binder-free supercapacitor electrodes.Additionally,the Ti@α-Fe2O3 and Ti@β-Fe2O3 nanoarrays are synthesized through thermal treatment.Such Ti@Fe OOH nanoarrays displayed a good specific area capacitance and lower resistance.These favorable performances suggest that the Fe OOH nanoarrays on Ti grid is a promising electrode material for supercapacitors.(2)Synthesis and supercapacitive properties of Mn O2-Ti O2-decorated carbon cloth paper nanocompositesTitania-based nanostructures and porous Mn O2 layer are stepwise deposited onto carbon fiber paper(CFP)conductive support using hydrothermal method.Ti O2 nanoparticles and leaf-like Na2Ti3O7 nanosheets are synthesized through the hydrolysis of Ti F4 and post-treatment in Na OH aqueous solution.Electrochemical tests reveal that CFP@Ti O2@Mn O2 has a better performance with areal specific capacitance of 744 m F cm-2 at 0.25 m A cm-2,compared with that(600 m F cm-2)of CFP@Na2Ti3O7@Mn O2.The possible mechanism is that Ti O2 has higher surface area and better electronic conductivity than those of Na2Ti3O7.However,the cycling performance of CFP@Ti O2@Mn O2 is limited with capacitance retention of 17.7% after 1000 cycles while CFP@Na2Ti3O7@Mn O2 keeps this retention up to 54.9%.(3)Controlled fabricating strategies of Ti O2-based nanocompositesDiverse Ti O2-based nanocomposites have been successfully prepared via biphase method,self-assembly,and/or one-pot hydrothermal method.For instance,we have developed a one-pot preparative route to fabrication Au-Ti O2 nanocomposites via Lysies.Interestingly,bifunctional surfactants play a vital role for such unique hybrids.Lysies induces the formation of Au nanoparticles and Ti O2 nanorods in one step due to its bifunctional bonds.The effects of detailed preparative parameters(e.g.,processing time and ratio of Au/Ti O2 precursors)on hybrids’ morphology are also examined to clarify their functions.Furthermore,we have developed a one-pot chemical approach to fabricate crystalline anatase Ti O2 onto graphene oxides with controlled Ti O2 distribution.Possible formation mechanism of such architecture is addressed.Interestingly,Ti O2 nanocrystals can be anchored within detached GOs,which could provide high surface area and close connection between both components to promote ions penetration and electron transport in promising energy conversion and storage applications.In addition,we have developed a facile and large-scale bottom-up approach to fabricate Au-Ti O2 binanoparticles monolayer onto graphene oxides with controlled distribution.Fabrication pathways of such architecture are addressed.Interestingly,Au-Ti O2 nanocrystals can be anchored and interweaved on the surface of GOs to increase the specific surface area and improve their stability.Moreover,we have developed at wo phase wet chemical approach to fabricate crystallineanatase Ti O2 Within hollow manganese dioxides.Interestingly,Mn O2 nanocrystals can be tuned into hollow structures with Ti O2 nanoparticles inside,which could provide high surface area to enhance the adsorption efficiency and to promote electron/hole separation and electron transportin promising photocatalysis.Additionally,we have developed a one-pot preparative route to fabricate Mn O2 nanosheet arrays on surface modified titanium grids.Well-controlled fabrication pathways of such architecture are addressed.To conclude,several facile preparative routes have been developed for Ti O2-based nanocomposites,which could be used to fabricate promising electrode materials for supercapacitors.Such strategies could also be extended to other high-value nanocomposites(e.g.,biphasic method)for various applications.